tach wiring '71 cuda ralley dash

[Got JOB]

How is the tach wired  in the wiring harness? Where does it get 12 volts?

[FY1Cuda]

On a '70 (and probably a '71), the tach gets  the power from a blue wire that is tapped off of the radio plug.  The radio plug has two sides to it: one is for powering the radio and one is for the light on the face of the radio.  The blue tach wire is spliced off of the orange lighting side of the plug.

[Chryco Psycho]

you sure , that would mean the only time the tach would have is is when the lights are on 

[JayBee]

I just looked at my service manual's schematic at it shows the blue wire tapping off the radios red w/tracer wire (X12-18R*).

[FY1Cuda]

I stand corrected.